1. Field of the Invention
The present invention relates to a mobile communication system, a relief method of competition between a Down Link RRC message and inter-cell movement of user equipment, and a radio network controller.
2. Description of the Prior Art
In a mobile communication system constructed of a radio network controller (RNC) which has a Radio Resource Control (RRC) layer and a Radio Link Control (RLC) layer, which are defined in the 3rd Generation Partnership Project (3 GPP), and user equipment (UE), the user equipment in a CELL_FACH state can communicate with only a specific cell.
In addition, there is a processing method of securing a radio resource, which is distributed under a situation that an RRC supported by a mobile unit is not converted to a operating state from a pause state, not to be released carelessly (e.g., refer to Japanese Patent Laid-Open No. 2004-159297).
Nevertheless, since user equipment in a CELL_FACH state can receive a Down Link message only from one specific cell, the user equipment transfers a with-in range cell of itself to a radio network controller by CELL UPDATE processing when movement between cells arises. By this, a radio network controller can send a DL message for the user equipment to a cell. However, when the competition processing arises in the timing when a DL message, which a radio network controller transmits, and inter-cell movement of user equipment are almost simultaneous, that is, when the radio network controller has transmitted the DL message to an old cell before cell update procedure from user equipment which becomes a trigger is completed, the user equipment cannot receive the DL message.
Here, in the 3 GPP, in message transmission between user equipment and a radio network controller, an RLC acknowledged mode (RLC AM) which performs acknowledgment of the transmission in an RLC layer is defined. Therefore, when user equipment moves to another cell before the user equipment receives an RLC AM message which a radio network controller has transmitted, the radio network controller cannot receive RLC ACK which is a response to the message.
In this case, although RLC resending is performed up to a number of RLC AM_DATA resending (Max DAT) in the RRC layer of the radio network controller, when a number of RLC resending exceeds the above-mentioned number of resending, that is, when user equipment has already moved to another cell, a high order RRC layer is notified of an RLC alarm. In conventional processing, since RLC states between the user equipment and radio network controller become unmatched in the case of a CELL_FACH state by RLC alarm reception, the call is released.
Up to now, since acknowledgment could not be performed when a radio network controller transmitted an RLC AM, an RLC state became mismatched and the call was released. Nevertheless, the present invention aims at providing a relief method of competition between a Down Link RRC message and inter-cell movement of user equipment in a mobile communication system which can continue communication by resetting RLC and resending the RRC message if necessary.